The following account of the prior art relates to one of the areas of application of the present invention, audio transmission to a hearing aid.
Previously audio transmissions over Bluetooth have been focused on, either low latency, low quality, voice transmission for phone calls, or high latency high quality transmission for entertainment. These solutions are known from the Bluetooth profiles ‘Headset’ and ‘Hands-Free’, respectively, which both are designed for phone use, and the A2DP profile (A2DP=Advanced Audio Distribution Profile), which is designed for music.
Recently the rise of 3 G telephony has driven the development of higher quality, low latency transmission within the Bluetooth SIG (SIG=Special Interest Group). This has resulted in the drafted Wideband speech profile, which is based on the frame based SBC codec (SBC=Low Complexity Subband Codec, an audio codec providing compression with inherent loss of data) known from the A2DP profile of the Bluetooth standard transmitted over the low latency SCO connection (SCO=Synchronous Connection-Oriented), which again is known from the Hands-Free profile of the Bluetooth standard.
US 2008/0013763 A1 describes a system for wireless audio transmission with a low delay from a transmission device (e.g. a TV-set) to a hearing device. The audio data are transmitted in a Bluetooth signal, and the transmission device comprises a hearing-aid-specific coder for compressing the audio data before its transmission. The system further comprises a relay station for converting the Bluetooth signal from the transmission device into a signal for inductive transmission to the hearing device. In the relay station, no recoding is performed during the conversion. The transmission device transmits in accordance with the Bluetooth A2DP protocol. The hearing-aid-specific coder has a lower sampling rate than the standard Bluetooth coder SBC.
US 2008/0013763 A1 is limited to the Bluetooth A2DP profile and focused on eliminating the delay caused by the trans-coding required to transfer audio between the two wireless links. A2DP requires the support of both 44.1 kHz and 48 kHz sampling rates in stereo, which can both be difficult to fit into a near field (inductive) link with relatively low bandwidth.
US 2007/0086601 A1 describes a flexible air interface protocol for a hearing aid system, the protocol including a frame synchronization word to delineate the start of a frame structure.
US 2007/291723 A1 deals with aligning PCM audio data with RF time slots of a WLAN interface (e.g. Bluetooth).